Multistage re-emission amplifier



Aug. 18, 1936. w. G. H. FlNcH MULTISTAGE RBI-EMISSION AMPLIFIER FiledDec. 31, 1935 I I INVEINTORJ 3% iam ATTORNEY.

Patented Aug. 1936 electrical signals, the conventional amplifier ar--UNITED T PATENT OFFICE norms-race 2,051,693 nn-nmssron AMPLIFIER.

, William G. H. Finch, New York, N. Y. Application December 31, 1935,Serial No; 56,946

I 8Claims.

This invention relatesj -to electronic amplifier tubes and moreparticularlyto multi-sta'ge amplificatio'n utilizing re-emissioncharacteristics .within a single envelope.

In order to provide high amplification'for weak rangements provide forcascaded stages of ordinary amplifier tubes coupled by impedanceelements. In the amplification of photo-electric currents for example,the useof the high resistance coupling between the photo-electric tubeand the first amplifier stage introduces extraneous noises to thesignal. The ordinary circuit noises due to thermal agitation,shot-effect and the like, limit the signal-to-noise ratio obtainable.

Recent attempts have been made to employ the so-called secondaryemission or re-emission characteristics of electronic tubes forrelatively noiseless and high gain amplification within a singleenvelope. The Patent No. 1,903,569 to K. W. Jarvis and R. M. Blair ofApril 11, 1933 disclosesa ,multi-stage amplifier within a single tubewherein the electrons impinging upon specially prepared electrodesurfaces dislodge a correspondingly greater number of secondary,electrons, which in turn are directed to the next adjacent electrode forcumulative re-emission amplification. The original signal is accordinglysuccessively amplified by successive dislodgment of increased number ofsecondary electrons along the multielectrode path cascaded within thetube.

The elimination of impedance coupling between electronic amplifierstages reduces thermal circuit noises of .the amplifier. By arranging aplurality of re-emission amplification stages in series within a. commonenvelope, enormous amplification of weak electrical signals is feasible,The comparatively wide spacing between the electrodes reduces theinterelectrode capacitance between them permitting a wider range-offrequencies to be amplified by this method as compared to conventionalmethods.

For the eificient operation of a multi-stage reemission amplifier, it isnecessary to separate the electrons impinging upon an electrode fromthose dislodged and emitted therefrom. It is also necessary that theelectrons due to secondary emission be directed or focused upon thesucceeding electrode. The prior art employs electrodes which are flatand arranged in complicated manners to provide the focusing action. I amaware,

preferred embodiment .art. A direct curent potential feature of mypresent invention to direct the reemitted electrons to the nextsucceeding electrode in a three. dimensional cycloidal path .having'apredetermined pitch equal to the distance between adjacent electrodes ashereinafter described in more detail.

It is accordingly an object of my present invention to provide a. novelconstruction of multistage re-emission amplifiers.

It is another object of my invention to' provide a novel electron beamfocusing arrangement for reemission I amplifiers.

It is a further object of my present invention to provide a novel,cheap, simple and efiicient multi-stage re-emission amplifier.

These and other objects of my invention will become apparent inthefollowing description in connection with the drawing in which:

Figure 1 is a partial sectional elevation of a sion amplifier tube witha schematic circuit diagram employing it. a

Figure 2 is a top view of the portion of the tube I containing a. windowto admit light.

Figure 3 is a schematic illustration for describing the electronicaction of the tube. y

In carrying out my invention, I employ a cylindrical glass envelope l0having a glass rod H secured centrally between the envelope seals l2 andI3. A circular electrode i4 is mounted near one end of the axial post II. The outside surface of the electrode I I is coated with aphoto-sensitive'substance. A plurality of circular electrodes l5 aremounted along the'central ro'd ll spaced from each other in apredetermined manner.

The electrodes are interconnected by resistances of relatively highvalue, of the order of 100,000 ohms, toprovide electrical continuitybetweenthem and to maintain the electrodes at successively higherelectrostatic potential levels. In a preferred arrangementJ use a carbonor graphite composition It applied around the central tube l Iinterconnecting the electrodes. Compositions for such a resistivecoating iii are well known in the source I! applied the necessaryelectrostatic potential to. the electrodes. The photo-sensitive cathodei4 is connected to the negative side of the battery II by connection l8.The next to the last electrode lid is connected to the positive side ofpotential source I! by lead IS. A series circuit is accordingly had fromthe negative side of battery I! to photosensitive cathode I through leadl8, through resistive coatings l6 and electrodes IS-in succession to theelectrode 15a and back to the positive side of the battery through leadIS. A small circulating currentwill flow in this series circuit, and thepotential drop across the resistances l6 will cause the electrodes-i5 tohave corresponding of a multi-stage re-emis 20 determined manner. Thevoltage of the source I! should be sumciently high so as to be equal tothe sum of the differences in potential between all the cascadedelectrodes. The electrostatic difference in potential between the twoadjacent electrodes is preferably of the order of 100 to 400 volts.

There is no resistive coating between the last electrode l5b and thenext to last electrode l5a. Electrode I5!) is connected externally bymeans of lead 20 to one side of a load circuit or-translation device 2|.The other side of the load circuit is connected to the positive side ofthe potential source 22, the negative side of which is connected to theprevious electrode l5a by means of lead I9. The voltage of potentialsource 22 is preferably substantially equal to the voltages between thesuccessive electrodes IS.

The electrodes l5 are specially prepared with a surface particularlyadapted for secondary electron emission. Such surfaces are alreadyestablished in the art and may, for example, be a silver-oxide layerhaving a further layer of caesium combined therewith. Such a. surface issomewhat similar to that used in some types of photo-electric tubes andis accordingly photosensitive also. .Such a surface will easily releaseelectrons when impinged by primary electrons, the ratio of the secondaryor re-emitted electrons to the primary electrons being dependent uponthe velocity of the-primary electron at impact. An emission ratio offive, for example, means that five secondary electrons will be dislodgedor emitted from the electrodes l5 for each primary electron impingingthereon. The glass envelope I0 is preferably highly evacuated. Thesurface of the glass is preferably darkened to prevent extraneous lightfrom reaching the electrodes. A transparent opening is arranged abovethe photo-sensitive electrode l4 so that light may be focused upon it.

The solenoid 23 wound on an insulation form 24 encloses the cylindricaltube ID. The ends of the solenoid 23 project sufficiently beyond the endelectrodes H and I5!) so as to provide a substantially uniform magneticfield within the en,- velope l0 and between the end electrodes. Solenoidwinding 23 is connected to a direct current source 26 in series with arheostat 21 used to adjust the current therethrough. A predeterminedmagnetic field accordingly is adjustable about the electrodes of themulti-stage re-emission amplifier according to my invention. Thismagnetic field has a uniform intensity across the tube sectionperpendicular to its axis, as well as axially along the'tube. Thismagnetic field, as will be hereinafter described in detail, is theprin-.- cipal electron ,beam focusing agent and is the basis of mypresent invention.

An oval window'25 in the insulated coil form 24 is arranged above thephoto-sensitive electrode It as illustrated in Figure 2. The windowconstruction permits the light to be directed upon the electrode H inorder to provide the signal energy which is to be amplified by the tube.I have illustrated a variable light source 28 in Figure 1 which emits alight signal 29 to schematically represent anysignal light source whichis to be amplified as corresponding electrical signal energy. A lenssystem 30 focuses the light signal 29 upon the photo-sensitive cathodeId.

The variable light source28 may, for example, ho facsimile signals whichwould ordinarily be directed to the photoelectric tube of ordinaryequipment. Electrons will be emitted from the cathode I4 and beattracted to the electrode l5 which may, for example be at apotential'of 200 volts higher than the electrode 14. The magnetic fieldis effective around the electrodes and in a direction parallel to theaxis of the tube. This magnetic field is substantially uniform acrossthe section of the tube as well as axially. The strength of the magneticfield and its polarity is arranged so as to act upon the emittedelectrons I to focus them or otherwise direct them to the nextsucceeding electrode I5. The electrons impinging upon the succeedingelectrode l5 willin turn act as primary electrons and will dislodgecorresponding secondary electrons greater in number by the emissionratio. These re-emitted secondary electrons will in turn be directed tothe next succeeding electrode in a similar manner.

In Figure 3, I have schematically illustrated the action which ischaracteristic of the reemission amplifier according to my invention.When the electrode l5 emits an electron it will travel to the nextsucceeding electrode l5" along a three-dimensional or space curve 3|.The path of the curve 3| is determined by the electrostatic. differenceof potential between the adjacent electrodes l5' and IS", the strengthof the magnetic field surrounding these electrodes and the initialdirection of the emitted electron. The path 3| is fundamentallycycloidal in character but also has a helical or spiral component sincethe operation is not in a single plane but extends around the tube. Thedistance between the points from which the electron leaves one electrodeand at which it impinges upon the next succeeding electrode, I shallterm the pitch of the space curve traversed.

The pitch of the space curve is definitely related to the strength ofthe magnetic field and to the axial component of the velocity of the.electrons, which in turn depends upon the voltage between the successiveelectrodes. The radial amplitude of the space curve depends upon theangle at which the individual electron is dislodged or' emitted from theelectrode surface. The magnetic field produces the focusing energy whichresults in the emitted or secondary electrons to be focused upon thenext succeeding electrode since it imparts to the radially directedelectrons the proper velocity components to cause it to be focused uponthe succeeding electrode.

The electron travelling along path 3| will therefore impinge upon theelectrode l5" at a velocity sufilcient to dislodge severa secondaryelectrons which will travel in paths 32, 33 and 34. I have illustratedin Figure 3, three such re-emitted electrons for simplicity. Theseelectrons travel in a spiraled cycloidal path to the next succeedingelectrode |5"'. These electrons do not travel overa common path since,in general, their directions of emission are not the same. However, thecharacter of their path and their pitch or dis;- tance of axial movementare predetermined to cause them to impinge upon the next electrode |5".Each impinging electron will in turn act as a primary electron upon theelectrode l5' and in turn cause a number of secondary electrons to beemitted due to its impact. I have illustrated a plurality of individualpaths 35 of such electrons emitted from the electrode l5"" which in turnare directed to the next succeeding electrode (not shown) to repeat theaction.

It will be obvious that for each electron emitted I at the initialelectrode M, a corresponding increased number of electrons will result'at the final electrode of the series arrangement. The ratio of thefinal number of electrons to the initial emitted electrons of theprimary emitter, namely electrode It, depends uponthe number of stagesemployed as well as the operating parameters used. When a strong lightsignal impinges upon the photosensitive surface H, a correspondinglylarger number of electrons are initially emitted therefrom, producing anincreased output current proportional thereto. The action of themulti-stage re-emission amplifier is linear and that obtainableheretofore. Extremely high amplification is feasible utilizing only onemultistage tube as illustrated. By employinsa surface of low workfunction for the anode electrodes so that a relatively larger number ofsecondary electrons are emitted for eachprimary impinging electron, andby employing electronvelocities to cause a higher ratio ,of suchemission, the cumulative action of the re-emitted electrons will resultin an extremely high amplification with apractical or nominal number ofstages within a single envelope. The constant magnetic field coactingwith the progressively increasing electrostatic field along the tubeserves to direct the electrons in a positive predetermined mannerbetween adjacent electrodes along a spiraled cycloidic path having thesame pitch as the electrode spacing. Although I have illustrated theprinciple of my invention utilizing a photosensitive primary emitter orelectron source, namely, the cathode ll, it will be realized that athermionic cathode may equally well be employed. In such case the actionofv the tube spirit and scopev thereof may be controlled by suitableinserted grids or latticed electrodes sible to modulate the otherwiseconstant electron stream by inserting a modulation or signal in serieswith the solenoid 23 circuit. The action of the modulation signal is tochange the pitch of the electron paths between the successive electrodesso that a proportionate number of electrons will fall short of or passbeyond the elec-- trodes it ordinarily should impinge, in turnproportionately decreasing the output current in accordance with themodulation.

Although I have described in detail one particular modification of myinvention, .it will be obvious to those skilled in the art that changestherein are feasible that fall within the broader and I, therefore, donot intend to be limited except as set forth-in the appended claims.

I claim: f

1.- A muiti-stage electronic amplifier tube comprising an elongatedglass envelope: a glass rod supported axially in said envelope; aplurality of spaced secondary emissive electrodes of finite lengthmounted upon said rod:

. electron emitter mounted at one end of said similar to embodimentsalready established in the art. However, it is posondary.axisliywithinsaid aprimary rod and ee meansmsaidrodintsr. I connectingadjacent electrodes.

2. A multi-stage electronic amplifier tube comprising an elongated glassenvelope; a glass rod supported axially in said envelope: a plurality ofequi-spaced secondary emissive electrodes mounted on said rod; a primaryelectron emitter mounted at one end of said rod; resistance means coatedon said rod connecting adjacent electrodes, and a solenoid wound aboutsaid envelope. v

3 A multi-stage electronic amplifier tube comprising an elongated glassenvelope; a glass rod supported axially in said envelope; of equi-spacedmounted on said rod; a photo-sensitive cathode mounted on-one end ofsaid rod; resistance means on said rod connecting adjacent electrodes;and a solenoid velop'e.

4. A multi-stage electronic amplifier tube com:- prising an elongatedglass envelope; a glass rod supported axially in said envelope: aplurality of equi-spaced secondary emissive electrodes mounted on saidrod: a photo-sensitive cathode mounted at one end, of said rod;resistance means on said rod connecting adjacent elecsecondary emissiveelectrodes wound about said am trodes; a solenoid wound about saidenvelope;

and a window in said solenoid for admitting lightsignals to saidphoto-sensitive cathode.

- 5. A multi-stage electronic amplifier tube comprising an elongatedglass envelope; supported axially in said envelope; a plurality ofvequi-spaced secondary emissive electrodes mounted on said rod; a primaryelectron emitter means coated onsaid rod connecting adjacent electrodes;a solenoid wound about said enve- 9 output terminals for the amplifier.

8. A multi-stage electronic amplifier tube comprising an envelopehousing a primary electron emitting electrode, a plurality of spacedsecondary emisslve electrod means for producing a magnetic fieldlongitudinally of said electrodes 1 to form a spiraled cycloidal pathfor electrons between successive electrodes, said secondary 'emissiveelectrodes being located at the focal points of said spiraled cycloidalelectron path.

'7. A multi-stage electronic amplifier tube comprising an envelopehousing a primary electron emitting electrode, a rod mounted within saidtube, a plurality of spaced secondary emissi've electrodes mounted onsaid rod, means for producing a magnetic field longitudinally of saidelectrodesto form a, spiraled cycloidal path for electrons betweensuccessive electrodes, said secemissive electrodes being located at thefocal points of said spiraled cycloidal electron 8. A multi-stageelectronic amplifier tube comprising an eiongatedenvelope housing aphotoemissive electrode, an insulation rod mounted tube, a plurality ofspaced cylindrical secondary emissive electrodes mounted concentricallyon'said rod, a resistive coating on said rod intermediate and connectingadiacent electrodes, means for producing a magnetic field longitu ly orsaid electrodes to form a spiraled cyeloidal path for electrons betweensuccessive electrodes, said secondary emisslve electrodes being locatedat the focal points of said spiraled cycloidal I electron path.

a glass rod the last two adjacent electrodeshaving WILIIAMG.H.FINCH.

35 mounted at one end of said rod; resistance

